Communication networks typically operate in accordance with a given standard or specification which sets out what the various elements of the network are permitted to do and how that should be achieved. For example, the standard may define whether the user or more precisely, user equipment is provided with a circuit switched service or a packet switched service. The standard may also define the communication protocols which shall be used for the connection. The given standard also defines one or more of the required connection parameters. The connection parameters may relate to various features of the connection. The parameters may define features such as the maximum number of traffic channels, quality of service and so on or features that relate to multislot transmission.
In other words, the standard defines the “rules” and parameters on which the communication within the communication system can be based on. Examples of the different standards and/or specifications include, without limiting to these, specifications such as GSM (Global System for Mobile communications) or various GSM based systems (such as GPRS: General Packet Radio Service), AMPS (American Mobile Phone System), DAMPS (Digital AMPS), WCDMA (Wideband Code Division Multiple Access) or CDMA in UMTS (Code Division Multiple Access in Universal Mobile Telecommunications System) and so on.
The user equipment i.e. a terminal that is to be used for communication over a particular communication network has to be implemented in accordance with the predefined “rules” of the network. A terminal may also be arranged to be compatible with more than one standard or specification, i.e. the terminal may communicate in accordance with several different types of communication services. These user equipment are often called as multi-mode terminals, the basic example thereof being a dual-mode mobile station.
A communication network is a cellular radio network consisting of cells. In most cases the cell can be defined as a certain area covered by one or several base transceiver stations (BTS) serving user equipment (UE), such as mobile stations (MS), via a radio interface and possibly connected to a base station subsystem (BSS). Several cells cover a larger area, and form typically a radio coverage area referred to as a location area (LA) or in some standards as a routing area (RA). It should be appreciated that the size of the location area or routing area depends on the system and circumstances, and may equal to one cell or be even smaller, such a part of a coverage area of a base station. A feature of the cellular system is that it provides mobility for the mobile stations, i.e. the mobile stations are enabled to move from a location area to another, and even from a network to another network that is compatible with the standard the mobile station is adapted to.
The user equipment (UE) within one of the cells of the cellular system can be controlled by a node providing controller function. Examples of the controller nodes include a base station controller (BSC), a radio network controller (RNC) and a mobile switching center (MSC), but other control nodes may also be implemented in the network. For example, in the circuit switched GSM (Global System for Mobile) network the controller node is provided by means of a mobile switching center (MSC). In the packet switched UMTS the radio access network thereof is controlled by a radio network controller (RNC). The controller can be connected further to a gateway or linking node, for example a gateway GPRS support node (GGSN) or gateway mobile switching center (GMSC), linking the controller nodes to other parts of the communication system and/or to other communication networks, such as to a PSTN (Public Switched Telecommunications Network) or to a data network, such as to a X.25 based network or to a TCP/IP (Transmission Control Protocol/Internet Protocol) based network. The network may also include nodes for storing information of mobile stations subscribing the networks or visiting the networks, such as appropriate home location registers (HLR) and visitor location registers (VLR).
When user equipment communicates with a communication network, a communication path has been established between the user equipment and an element or node of the network. The network node is typically one of the controller nodes. At least a part of the communication between the user equipment and the actual destination node will then pass through the controller node.
It is possible to transfer i.e. to handover the connection from a first node to a second node. This shall also be possible between two nodes that belong to different network systems. For example, a user equipment having a packet switched (PS) connection with a packet switched network system (e.g. the UMTS) may be handed over to have a circuit switched (CS) connection with a circuit switched network system (e.g. the GSM) and vice versa. The handover of the connection may be required e.g. when the mobile station moves i.e. roams from a cell to another cell. In case the new cell is not served by the same system as the pervious cell, the handover needs to be accomplished between different communication systems.
The inventor has found that in situations where a handover is to be accomplished between the nodes of different communications systems (i.e. systems that are based on different communication rules), it is possible that the “new” connection cannot be properly set-up due to a difference in the parameters required for the connection by the “new” and the “old” i.e. previous communication systems. An example is a handover from a packet switched connection to a circuit switched connection or vice versa. A more detailed example is a handover of a high speed circuit switched data connection between from UMTS (Universal Mobile Telecommunications System) to GSM (Global System for Mobile communications). In the GSM the high speed data is enabled by a multislot mechanism which requires a certain parameter to be exchanged at the call setup. A corresponding mechanism does not exist in the UMTS, and consequently corresponding parameters are not generated or exchanged at the UMTS-call setup. After a UMTS to GSM handover the multislot parameters, however, are required in the GSM portion of the call. Although the mobile stations may provide these parameters, the (dual-mode) UMTS mobile stations may not be obliged to send any GSM-specific parameters every time they se-up a UMTS-call, and therefore the parameters may need to be provided in some other manner at the intersystem handover. In addition, the tight timing requirements of handovers may not allow any exchange of parameters that are not used by the connection before or during the handover procedure.